1. Field of the Invention
The present invention relates to a conductive paste used for forming electrodes of electronic components, and to a laminated ceramic electronic component using the conductive paste. In particular, the present invention relates to a conductive paste appropriately used for forming internal electrodes of a monolithic ceramic capacitor, and to a monolithic ceramic capacitor in which internal electrodes are formed using the conductive paste.
2. Description of the Related Art
Laminated ceramic electronic components, for example, monolithic ceramic capacitors, have hitherto been primarily composed of ceramic laminates, internal electrodes, and terminal electrodes. The ceramic laminate is produced, for example, by baking a green laminate in which a plurality of green ceramic layers made of dielectric material are laminated. The internal electrodes are arranged between ceramic layers in the ceramic laminate, and are produced by the concurrent baking of a conductor paste applied on a plurality of green ceramic layers by printing and the green ceramic layers. Each of the end edges of the internal electrodes is formed so as to be exposed at one of the end faces of the aforementioned ceramic layers. The terminal electrodes are produced by baking a conductive paste applied by coating to the end faces of the ceramic laminate so as to connect to the internal electrodes exposed at the end faces of the ceramic laminate.
In order to form the internal electrodes of the aforementioned laminated ceramic electronic component, a conductive paste has been used. As the conductive paste, a paste in which a fine conductive powder made of Ni, Cu, Ag, Pd, etc., is dispersed in an organic vehicle composed of an organic binder and a solvent has been used.
In the case where a fine conductive powder having a particle diameter of 1.0 xcexcm or less is used for the conductive paste, the viscosity of the paste increases with time after production due to coagulation of the conductive powder. As a consequence, when this paste is applied by printing on a green ceramic layer using a screen printing method, etc., the film thickness of the printed coating film is likely to fluctuate. When the film thickness of the coating film is uneven, there has been a problem that delamination and cracks are likely to occur in the ceramic laminate produced by baking due to unevenness in volume change.
As an effective method for uniformly dispersing the aforementioned fine conductive powder in the paste, a method in which a dispersing agent is added in the paste can be mentioned. That is, since the surface of the conductive powder of Ni, Cu, etc., is basic, in consideration of, for example, interaction between acid and base, a method in which an anionic macromolecular dispersing agent is added can be mentioned.
By adding the dispersing agent into the paste, wetting of the conductive powder with the solvent is accelerated and a uniform mixture can be formed in a short time. However, the adsorption sites of the macromolecular dispersing agent are likely to form a three-dimensional cross-linking structure with not only one particle, but also a plurality of particles. When such a cross-linking structure is formed, an increase in viscosity of the paste and gelation of the paste are brought about. As a measure for improvement, the inventors of the present invention have discovered a method in which an amine surfactant is further added into a paste in order to mask excessive adsorption sites of an anionic macromolecular dispersing agent, as described in Japanese Patent Application No. 11-180450.
However, since the amine surfactants have, in general, high burning temperatures of about 300xc2x0 C., even when the aforementioned conductive paste is applied by printing on the green ceramic layers and this is dried sufficiently, the amine surfactant is likely to remain in the coating film after printing. In baking the green ceramic laminate in which a plurality of green ceramic layers provided with the aforementioned electrode dried films are laminated, when a temperature raising rate is increased during defatting, the amine surfactant remaining in the coating film is burned so as to rapidly generate gases. The gas generation causes the volume of the ceramic laminate to expand, and a problem may occur in that peeling is likely to occur at the interface between the internal electrode and the ceramic layer.
The present invention was made in order to solve the aforementioned problems. Accordingly, it is an object of the present invention to provide a conductive paste in which increase in viscosity with time is prevented and gas generation can be reduced during defatting, and a laminated ceramic electronic component.
In order to achieve the aforementioned objects, according to an aspect of the present invention, a conductive paste composed of a conductive powder having an average particle diameter of about 1.0 xcexcm or less, an organic vehicle, an anionic macromolecular dispersing agent, and an amine having a boiling point of about 120xc2x0 C. or more, but about 220xc2x0 C. or less, is provided, wherein the amine constitutes about 0.1% to 5% by weight of 100% by weight of the conductive paste.
The amine in the conductive paste according to the present invention preferably includes at least one tertiary nitrogen atom.
The conductive powder in the conductive paste according to the present invention preferably includes at least one powder selected from the group consisting of a Ni powder, a Cu powder and a powder of an alloy thereof.
According to another aspect of the present invention, a laminated ceramic electronic component composed of a ceramic laminate produced by laminating a plurality of ceramic layers and a plurality of internal electrodes formed between the ceramic layers is provided, wherein the internal electrodes are formed using the conductive paste according to the present invention.